1. Field of the Invention
The present invention relates to a method and an apparatus for generating three-dimensional shape data indicative of a shape of a workpiece to be obtained after machining on the basis of an NC program for an NC machine tool.
2. Description of the Prior Art
NC machine tools are generally adapted to machine a workpiece by moving a tool under numerical control according to an NC program including tool traveling path and the like. The NC program is generated manually by a programmer and, at present, automatically by means of an automatic programming apparatus. The automatic programming apparatus sequentially performs an automatic determining process of tool to be used, an automatic determining process of cutting condition and an automatic determining process of machining sequence on the basis of design data (hereinafter referred to as “CAD data”) generated by a CAD (computer aided design), tool shape data, cutting condition data and the like for generation of programming base data, and then generates the NC program on the basis of the programming base data thus generated. The CAD data is three-dimensional shape data indicative of a final shape and dimensions of the workpiece to be obtained after the machining.
In some case, a machining factory receives only an NC program generated by a CAD and an automatic programming apparatus from a customer to perform a workpiece machining operation. Where the workpiece machining operation performed on the basis of the NC program by means of an NC machine tool fails to provide an expected workpiece shape, the machining factory cannot review CAD data (three-dimensional shape data) on the basis of the NC program and, hence, cannot change the workpiece shape. Therefore, the machining factory has to request the customer to modify the NC program. For the modification of the NC program, it is necessary to modify the CAD data by means of the CAD and perform various processes by means of the automatic programming apparatus. This requires much time before the machining factory receives the modified NC program, resulting in downtime of the NC machine tool and, hence, reduction in productivity.
Further, tool traveling paths cannot be changed for modification of the NC program because the three-dimensional shape data cannot be reexamined on the basis of the NC program, even if a trouble occurs such that a tool is brought into thorough contact with the workpiece in a pocket corner thereof during the machining to leave chattering marks on the workpiece.
It is therefore an object of the present invention to provide a method and an apparatus for generating three-dimensional shape data indicative of a shape of a workpiece to be obtained after machining on the basis of an NC program for an NC machine tool.